This invention relates to an optical printer head for an optical printer such as a color video printer or the like, and more particularly to an optical printer head adapted to substantially prevent generation of a ghost due to light reflected by a peripheral surface of a light passage hole formed through a filter holder for holding filters thereon so as to act as a light path.
An optical printer for forming a desired image on a record medium such as, for example, a color film or the like is known in the art. Typical one of such optical printers has a fluorescent luminous tube incorporated therein so as to act as a light source. The optical printer is so constructed that light emitted from the fluorescent luminous tube is guided through red, green and blue color filters selectively changed over, resulting in light of the three primary colors being obtained, which is then subject to writing on a record medium such as a color film or the like, leading to formation of a full-color image thereon.
Now, such an optical printer will be described with reference to FIG. 15. An optical printer generally designated at reference numeral 50 in FIG. 15 includes an optical printer head 100 which is reciprocated in a sub-scanning direction A with respect to a record medium W such as a color film or the like arranged at a predetermined position by transfer means 51. The transfer means 51 includes guide means (not shown) for guiding the optical printer head 100 in the sub-scanning direction A, a pair of pulleys 53 on which a drive belt 52 is wound in a manner to extend therebetween, and a drive motor 54 for rotating one of the pulleys 53. The optical printer head 100 is fixed on the drive belt 52 and the drive motor 54 is driven to circulate the drive belt 52, so that the optical printer head 100 is moved in the sub-scanning direction A while being guided by the guide means. The optical printer head 100 is received in a housing (not shown) together with the record medium W. A plurality of such color films each acting as the record medium W are held at a predetermined position and outwardly discharged while being interposed between carrier rollers 55 after they are subject to writing by means of light emitted from the optical printer head.
Now, the optical printer head 100 will be described more detailedly with reference to FIGS. 16 and 17. The optical printer head 100, as shown in FIG. 16, includes a fluorescent luminous tube 101 including a plurality of luminous dots for emitting linear light and acting as a light source and a filter holder 102 for holding a red color filter R, a green color filter G and a blue color filter B thereon. The fluorescent luminous tube 101 and the filter holder 102 are housed in a housing 103. Also, the optical printer head 100 includes a selfoc lens array 104 arranged above the housing 103 for forming incident light into an erected real image at an equi-magnification.
The housing 103, as shown in FIG. 16, is provided with an opening 105, which is mounted thereon with a bottom plate 106 while the fluorescent luminous tube 101 and filter holder 102 are kept received in the housing 103, so that the housing 103 and bottom plate 106 cooperate with each other to constitute a box-like base 107. The filter holder 102 is formed with a plurality of filter holding holes 108 in parallel to each other and in a manner to extend in a main scanning direction perpendicular to the sub-scanning direction A in which the optical printer head 100 is transferred. The color filters R, G and B are held in the thus-formed filter holding holes, respectively.
The color filters R, G and B are selectively changed over by sliding the filter holder 102 along an upper surface of a glass plate 101a of the fluorescent luminous tube 101 and a wall surface of an opening 105 of the housing 103 in the sub-scanning direction indicated at arrow A in FIG. 16, so that any desired one of red, green and blue colors may be selected. The selfoc lens array 104 is provided by constructing a plurality of selfoc lenses into a single module.
Unfortunately, the conventional optical printer head 100 constructed as described above causes an end of the upper surface of the glass plate 101a of the fluorescent luminous tube 101 to tend to be caught in the filter holding holes 108 for holding the color filters R, G and B therein as shown in FIG. 17, when the filter holder 102 is slid in the sub-scanning direction A to carry out changing-over among the color filters R, G and B.
Sliding of the filter holder 102 under such circumstances causes the filter holder to be shaved to produce dust, because it is made of a resin material. The thus-produced dust adheres to a surface of the color filters R, G and B. Adhesion of the dust to the filters keeps light emitted from the fluorescent luminous tube 101 from satisfactorily permeating through the color filters R, G and B, to thereby fail to permit the light to be formed into a normal image on the color film acting as the record medium W, leading to a deterioration in quality of the image.
Also, it is needed to replace the fluorescent luminous tube 101, when the fluorescent luminous tube 101 is deteriorated in function to a degree sufficient to fail to exhibit satisfactory performance. Such replacement requires to detach the bottom plate 106 from the housing 103. However, this causes the color filters R, G and B to be exposed to an ambient atmosphere, resulting in dust contained in an ambient atmosphere adhering to the color filters R, G and B, so that quality of the image is further deteriorated.
In view of the foregoing, the inventors proposed an optical printer head which is capable of solving the above-described problems. The optical printer head is also constructed in such a manner that filters are small-sized to provide a portable optical printer. Now, the optical printer proposed will be described with reference to FIGS. 18 and 19, wherein FIG. 18 is an exploded perspective view of the optical printer head and FIG. 19 is a sectional side elevation view of the head.
The optical printer head generally designated at reference numeral 1 in FIGS. 18 and 19, as shown in FIG. 19, is so constructed that only a filter holder 2 on which red, green and blue color filters R, G and B are held is received in a housing 3. Also, the optical printer head 1 includes a selfoc lens array (hereinafter also referred to as "SLA") 4 arranged above the housing 3 so as to form incident light into an erected real image at an equi-magnification, as well as a fluorescent luminous tube 5 arranged below the housing 3 so as to act as a light source.
The housing 3, as shown in FIG. 19, is formed with an inner space 3a which is open on a side of a rear surface of the housing 3. The housing 3 has an upper wall formed with an elongated communication hole or light passage hole 6 communicating with the inner space 3a in a manner to extend in parallel to a main scanning direction perpendicular to a sub-scanning direction A, as shown in FIG. 19.
The filter holder 2, as shown in FIG. 18, includes a flat section 2a and an operation element 2b. The flat section 2a is formed thereon with three elongated filter holding holes or light passage holes 7 (7a, 7b and 7c) so as to extend in a direction of arrangement of luminous dots 5a and 5b of the fluorescent luminous tube 5 described hereinafter and in a manner to be parallel to each other at equal intervals. The filter holding holes 7 each have a width in the sub-scanning direction A formed into a size sufficient to permit light emitted from the luminous dots 5a and 5b of the fluorescent luminous tube 5 to pass therethrough. The filter holding holes 7a, 7b and 7c has the color filters R, G and B held therein, respectively. The color filters R, G and B permit lights at predetermined wavelengths or red light, green light and blue light to permeate therethrough, respectively. The operation element 2b is connected to a drive mechanism (not shown) to slide the filter holder 2 in the sub-scanning direction A. The filter holder 2 is received in the inner space 3a of the housing while positioning any one of the color filters R, G and B above the luminous dots 5a and 5b of the fluorescent luminous tube 5 described below.
The housing 3, as shown in FIG. 19, is mounted on the opening of the inner space 3a thereof with a bottom plate 8 while receiving the filter holder 2 therein, so that the housing 3 and bottom plate 8 cooperate with each other to constitute a box-like base 9. The housing 3 has side surfaces acting to regulate a width of sliding movement of the filter holder 2. One of the side surfaces of the housing 3 is formed with a hole 3b through which the operation element 2b of the filter holder 2 is inserted. The filter holder 2 is abutted on one side surface thereof against a bottom surface of the housing 3 and on the other surface thereof against the bottom plate 8. The bottom plate 8 is formed with an elongated through-hole or light passage hole 10 in a manner to extend in the main scanning direction perpendicular to the sub-scanning direction A and be opposite to the communication hole 6, resulting in light emitted from the fluorescent luminous tube 5 being guided therethrough.
Selective changing-over among the red, green and blue color filters R, G and B is carried out by sliding the filter holder 2 along a wall surface of the space 3a in the sub-scanning direction indicated at the arrows A in FIG. 19.
The selfoc lens array or SLA 4 acting as image formation means is provided by constructing a plurality of the selfoc lenses 4a into a single module. The SLA 4 is formed by integratedly arranging the selfoc lenses 4a with high precision while rendering central axes 4b of the selfoc lenses 4a parallel to each other. The SLA 4 is then fixed on a circumference thereof to a frame plate 4c to constitute an optical element while being mounted on the housing 3 in a manner to be positioned above the communication hole 6 of the housing 3. The SLA 4 has an incident surface 4d located within a region of the communication hole 6 and facing the luminous dots 5a and 5b of the fluorescent luminous tube 5, to thereby form a light path in a direction perpendicular to the sub-scanning direction A. The selfoc lenses 4a each are formed into a substantially column-like shape and has a refraction index distributed in a manner to be parabolically reduced from the central axis 4b to an outer peripheral surface thereof.
The fluorescent luminous tube 5, as shown in FIG. 18, is constituted by a rectangular substrate 11 made of a light-permeable and insulating glass material and a box-like casing sealedly joined to the substrate 11, resulting in providing an envelope 13 of a substantially parallelepiped shape, which is evacuated at a high vacuum. The substrate 11 is formed on an inner surface thereof with a plurality of the luminous dots 5a and 5b acting as a luminous section, which are arranged in rows in a manner to be spaced from each other at predetermined intervals. In FIG. 18, the luminous dots are arranged in two rows in an offset or staggered manner. The luminous dots 5a and 5b each include an anode conductor and a phosphor layer of ZnO:Zn or the like deposited on the anode conductor. The luminous dots 5a and 5b are located within a region of the communication hole 6 and though-hole 10. The luminous dots 5a and 5b are juxtaposed to each other in the main scanning direction perpendicular to the sub-scanning direction A shown in FIG. 19 in which the optical printer head 1 is moved.
The optical printer head also includes filamentary cathodes (not shown) arranged below the luminous dots 5a and 5b so as to extend in the main scanning direction. The anode conductors of the luminous dots 5a and 5b are led out of the envelope 13 in a manner to be independent from each other and separately driven due to feeding of a drive signal thereto.
The fluorescent luminous tube 5 is so constructed that each of the luminous dots 5a and 5b and the central axis 4b of each of the selfoc lenses 4a are arranged in correspondence to each other so as to form a pair. The fluorescent luminous tube 5 thus constructed is detachably mounted on an outer surface of the bottom plate 8 using any suitable fixing means such as screws or the like while being received in a frame-like container 14 for the fluorescent luminous tube 5.
In the optical printer head 1 shown in FIGS. 18 and 19, when a width of the filter holding holes 7 defined in the sub-scanning direction A is set to be minimum while permitting light emitted from the luminous dots 5a and 5b of the fluorescent luminous tube 5 to permeate therethrough, a stroke of movement of the filter holder 2 can be reduced. This permits the optical printer head 1 to be small-sized to a degree sufficient to render the optical printer portable.
However, it was found that a reduction in width of the filter holding holes 7 in the sub-scanning direction causes serious problems.
More particularly, the selfoc lenses 4a of the SLA 4 of the optical printer head 1 each have optical characteristics which permit light incident at a maximum allowable incident angle .theta. predetermined for every lens in a direction of the central axis 4b of the selfoc lens 4a with respect to an incident surface 4d of the lens facing each of the luminous dots 5a and 5b of the fluorescent luminous tube 5 to be formed into an erected real image at an equi-magnification. The maximum allowable incident angle .theta. indicates an incident angle which permits light reaching the incident surface 4d of the SLA 4 to be incident on the SLA 4. For example, the maximum allowable incident angle .theta. is set to be 9.degree. in an SLA-9, 12.degree. in an SLA-12 and 20.degree. in an SLA-20.
Thus, as shown in FIG. 20, when light emitted from the luminous dots 5a and 5b of the fluorescent luminous tube 5 acting as the luminous section is incident on the incident surface 4d of the SLA 4 within the maximum allowable incident angle .theta., it is formed into an erected real image at an equi-magnification on the record medium or photosensitive medium such as a color film or the like positioned above the SLA 4. Thus, dot-like light emitted from the luminous dots 5a and 5b acting as the luminous section reaches the record medium W as it stands, resulting in a luminous dot image I being formed on the record medium. On the contrary, light incident on the incident surface 4d while being out of the maximum allowable incident angle .theta. fails to form an erected real image at an equi-magnification.
In FIG. 21, supposing that, of regions in which light is reflected by or on a peripheral surface of the filter holding hole 7 acting as the light passage hole, a region in which light is incident on the incident surface 4d within the maximum allowable incident angle .theta. constitutes a reflection region S as shown in FIG. 21; a portion of the peripheral surface of the filter holding hole 7 defined on a side of the fluorescent luminous tube 5 on the basis of the color filters R, G and B provides the reflection region S. In this instance, of light emitted from the luminous dots, light which is incident and reflected on the reflection region S is regarded as if it is directly incident on the incident surface 4d from a virtual luminous section 5c, resulting in generating a ghost g at a position apart from a luminous dot image I shown in FIG. 20.
The ghost g thus produced is increased in brightness or luminance in proportion to the real image, so that a bright flare-like portion appears in the form of an image on the record medium W, to thereby directly affect the image formed on the record medium W, leading to a deterioration in quality of the image.
In the optical printer head 1 constructed as described above, alignment between a center of the color filter R (G or B) and a light axis of the SLA 4 keeps light reflected on the peripheral wall of the filter holding hole 7 on a side of the SLA 4 on the basis of the color filters R, G and B from being incident on the incident surface 4d of the SLA 4 within the maximum allowable incident angle .theta..
The filter holder 2 is arranged so as to be movable in the sub-scanning direction A for selection of any one of the filters R, G and B. Such arrangement of the filter holder 2, as shown in FIG. 22, often causes the filter holding hole 7 to be somewhat deviated in the sub-scanning direction A from the central axis of the selfoc lens 4a due to a mechanical movement error. In this instance, the reflection region S in which light is incident on the incident surface 4d of the SLA 4 within the maximum allowable incident angle .theta. is likewise displaced to another reflection region S'. In FIG. 22, a portion of the peripheral surface of the filter holding hole 7 on the side of the SLA 4 on the basis of the color filters R, G and B defines the reflection region S'.
When light emitted from the luminous dot 5a is incident on the reflection region S', the light reflected is caused to be incident on the incident surface 4d of the SLA 4 within the maximum allowable incident angle .theta.. This results in the light being likewise regarded as if it is directly incident on the incident surface 4d from a virtual luminous section 5c', to thereby produce a ghost, which directly affects an image formed on the record medium W, leading to a deterioration in quality of the image.
Thus, when light emitted from the luminous dots 5a and 5b of the fluorescent luminous tube 5 is reflected by or on the outer periphery of the filter holding hole 7 and then incident on the incident surface 4d within the maximum allowable incident angle .theta., the ghost g is formed at a position deviated from the proper image formation position, to thereby cause a deterioration in quality of the image formed. Also, light emitted from the luminous dots 5a and 5b of the fluorescent luminous tube 5 is repeatedly reflected by or on the peripheral surface of the filter holding hole 7, so that the light reflected forms background light, to thereby cause a region other than the luminous dot image I to be increased in brightness or luminance, resulting in contrast of the image being reduced as a whole.